#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N = 100;
const int M = 1e9+7;

int t, n;
string s;

int main()
{
#ifdef LOCAL
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
#endif
    ios::sync_with_stdio(false), cin.tie(0);
    cin >> t;
    while(t--) {
        cin >> n >> s;
        
        bool start = false;
        for (int i = 0; i < n; i++) {
            if (!start && s[i] != '?') start = true;

            if (start && s[i] == '?') {
                s[i] = (s[i-1] == 'R') ? 'B' : 'R';
            }
        }

        start = false;
        for (int i = n-1; i >= 0; i--) {
            if (!start && s[i] != '?') start = true;

            if (start && s[i] == '?') {
                s[i] = (s[i+1] == 'R') ? 'B' : 'R';
            }
        }

        if (!start) {
            s[0] = 'B';
            for (int i = 1; i < n; i++) {
                s[i] = (s[i-1] == 'R') ? 'B' : 'R';
            }
        }

        cout << s << endl;
    }
    return 0;
}